[clang] [llvm] [AArch64] Implement the atomic store with hint intrinsic (PR #198316)

[Kerry McLaughlin via llvm-commits]

kmclaughlin-arm wrote:

> Hello Kerry ! The code looks good for me, but when using AI to identify issues with this patch, multiple issues popped up. I have checked them and they seem like valid concerns, which should be addressed before the patch is merged. Let me know what you think or if you have any issues with reproducing this!

Thanks for raising these issues @Lukacma . I've pushed a new commit to try to address each of them:

> ### P1: Stack-addressed hinted stores can crash frame-index elimination
- Added the `ATOMIC_STORE_HINT` pseudos to `getLoadStoreImmIdx()` & `getMemOpInfo()`. The order of address and data have also been swapped in the pseudo, as `rewriteAArch64FrameIndex` expects the immediate value to appear after the frame index. These changes are tested by atomic-store-pseudo.mir.

> ### P1: LFI object emission separates `stshh` from its store
- This is happening because the LFI MC rewriter inserts a guard (add instruction) immediately before the store. I've tried to defer emitting the stshh hint instruction until after the guard has been created by adding a `PendingMemHintInst`, with tests in atomic-store-hint.s.

> ### P1: `_Bool` and `_BitInt` use their scalar IR representation
- Bool types are now handled by `EmitAtomicStoreWithHintBuiltin` & BinInt types are rejected in SemaARM, which matches the behaviour of atomic stores without metadata. New tests added to arm_acle.c & builtins-arm64.c.
 
> ### P1: Array-to-pointer conversion is checked but discarded
- Fixed in SemaARM & tested in arm_acle.c.

> ### P2: Dependent and wide immediate arguments are mishandled
- Deferred checks of type or value dependent expressions in `BuiltinARMAtomicStoreHintCall` & added tests in atomic-store-hint-template.cpp.

> ### P2: Equivalent typedefs and volatile pointees are rejected
- Changed `SemaARM::BuiltinARMAtomicStoreHintCall` to compare underlying data types & set volatile on the new atomic store in `EmitAtomicStoreWithHintBuiltin`. Tested in arm_acle.c.

https://github.com/llvm/llvm-project/pull/198316